The present invention relates to a static frequency changer for feeding a synchronous machine, the changer being of the type including an intermediate direct current circuit between a static converter receiving energy from a mains and a static converter supplying power at the desired frequency to the machine side. A circuit of this type is disclosed, for example, in the text by Heumann and Stumpe, THYRISTOREN[Thyristors], published by B. G. Teubner, Stuttgart, 1969, at pages 130/131.
The reactive commutation power for the machine side static converter is here made available by the synchronous machine through its reactances. Therefore, the machine reactances must be designed to correspond to the required commutation duration.
Whereas synchronous machines having two or four poles have heretofore been used, there is a growing demand for synchronous machines having a larger number of poles in such static frequency changers. Such use has not occurred so far because the speed setting range has been too small and high speeds could not be achieved because of the long quenching periods required by the static converter switching elements as a result of the a.c. side commutation via the machine reactances. The frequency limit of the machine side static converter, when conventional thyristors are used as the static converter switching elements, is only about 75 Hz.